The use of high-power fiber-coupled lasers continues to gain popularity for a variety of applications, such as materials processing, cutting, welding, and/or additive manufacturing. These lasers include, for example, fiber lasers, disk lasers, diode lasers, diode-pumped solid state lasers, and lamp-pumped solid state lasers. In these systems, optical power is delivered from the laser to a workpiece via an optical fiber.
Various fiber-coupled laser materials processing tasks require different beam characteristics (e.g., spatial profiles and/or divergence profiles). For example, cutting thick metal and welding generally require a larger spot size than cutting thin metal. Ideally, the laser beam properties would be adjustable to enable optimized processing for these different tasks. Conventionally, users have two choices: (1) Employ a laser system with fixed beam characteristics that can be used for different tasks but is not optimal for most of them (i.e., a compromise between performance and flexibility); or (2) Purchase a laser system or accessories that offer variable beam characteristics but that add significant cost, size, weight, complexity, and perhaps performance degradation (e.g., optical loss) or reliability degradation (e.g., reduced robustness or up-time). Currently available laser systems capable of varying beam characteristics require the use of free-space optics or other complex and expensive add-on mechanisms (e.g., zoom lenses, mirrors, translatable or motorized lenses, combiners, etc.) in order to vary beam characteristics. No solution exists that provides the desired adjustability in beam characteristics that minimizes or eliminates reliance on the use of free-space optics or other extra components that add significant penalties in terms of cost, complexity, performance, and/or reliability. What is needed is an in-fiber apparatus for providing varying beam characteristics that does not require or minimizes the use of free-space optics and that can avoid significant cost, complexity, performance tradeoffs, and/or reliability degradation.
Goppold et al. of Fraunhofer IWS describe attempts to improve laser cutting of thick steel plates using a technique they call “Dynamic Beam Shaping” (DBS). As described, among other places, at pages 18 and 19 in Industrial Photonics, vol. 4, issue 3 (July 2017), DBS entails synchronization of the following two stages of movements. The first stage is the movement of the laser cutting machine relative to a laser beam, as defined by feed rate and workpiece geometry. The second stage is an additional, high-frequency galvanometer-controlled oscillation of the laser beam within the cut kerf. With respect to the second stage, Goppold et al. describe figure-8, side-to-side, front-to-back, and other types of beam movements intended to improve cutting quality (e.g., reducing dross attachment and oxidization) by distributing optical energy homogeneously within the cut material so as to optimize cut kerf. These attempts, however, employ expensive free-space optics and rely on scanning technology.